The material prepared in a material storage space is introduced in a mold cavity, for example arranged in a molding tool, via a gating system formed by a distribution system and a gate. The material solidifies in the mold cavity. The “gate” (i.e., “ingate” or “inlet port”) is that part of a gating system which connects the molded part (in the case of an injection molding machine also called the injection molded part) formed by the solidified material in the mold cavity with the distribution system.
There are different parameters for the description of the compression behavior of a compressible material, for example the compression modulus K which is exemplarily discussed in the following. However, the invention can also be realized with other parameters (such as the compressibility).
The compression modulus K of a material describes which all-sided pressure modification is necessary in order to cause a determined modification of the volume of the material. It is defined as:
                    K        =                              -            V                    ⁢                      dp            dV                                              (                  Equation          ⁢                                          ⁢          1                )            
V . . . volume
dp . . . (infinitesimal) pressure modification
dV . . . (infinitesimal) volume modification
dV/V . . . relative volume modification
In the following, plastic melt is discussed as an example for the processed material, and an injection molding machine is discussed as an example for a molding machine. The invention is not limited to one of these examples.
Pressure and volume of a plastic melt are two of the most important physical parameters when processing plastics in an injection molding process. Therefore, the compression modulus also has an enormous significance for the injection molding. The force applied onto the injection piston and the thus emerging pressure have the primary function to get the melt flowing and to thereby fill a molding tool cavity. By the required pressure, a volume reduction corresponding to the compression modulus occurs. The temporal modification of the screw position and the thereof calculated volume thus contains proportions which correspond to the volume flow in the cavity and proportions which have their origin in the compression of the melt. In order to detect and to distinguish these proportions, the knowledge of the compression modulus as well as the actually present melt volume is necessary.
A generic method is disclosed in the EP 0 478 788 A1 (Komatsu). In this Komatsu reference, the execution of a compression test is described with reference to therein indicated FIG. 7. The compression test is executed when the machine nozzle is closed at the position 30 and thereby considers the volume of the screw vestibule and the material designated with reference sign 6.